Polymeric additives derived from acrylic and methacrylic acids are extensively used in mineral lubricating oil compositions, particularly in automatic transmission fluids and crankcase oils, to impart desirable viscosity-temperature characteristics to the compositions. These additives are designed to modify lubricating oil so that changes in viscosity occurring with variations in temperature are kept as small as possible. Lubricating oils containing such polymeric additives essentially maintain their viscosity at the high temperatures normally encountered in engine and transmission operations while at the same time maintaining a desirably low viscosity fluidity at engine starting temperatures. The ability of the hydrocarbon oil to accommodate increased and decreased temperatures with a minimum change in viscosity is indicated by its Viscosity Index (VI). The greater this ability the higher the VI. Because of the aforementioned properties, these polymeric additives have been conveniently termed both "thickeners" and "VI improvers."
The increasing demands made by the present day engines and automatic transmissions due to increased antipollution and performance requirements have increased a need for crankcase and automatic transmission fluid additives which have multifunctional properties in order to prevent a buildup of such large quantities of additives required to meet the specification as to pose a danger of a quantity so large as to negatively effect the primary mission of the crankcase oil or transmission fluid. One class of additives that meets this requirement are the dialkylaminoalkyl-, C.sub.1 -C.sub.6 alkyl, C.sub.10 -C.sub.14 alkyl, C.sub.16 -C.sub.20 alkyl methacrylate interpolymers of a molecular weight of between 5.times.10.sup.4 and 10 .sup.6. These polymethacrylates not only provide improved VI properties to crankcase and transmission oils, but also have the properties of imparting improved dispersancy, low temperature fluidity and antioxidant properties thereto. The component which principally contributes to the improved detergent and antioxidant properties is the dialkylaminoalkyl methacrylate, the improvement generally in proportional relationship with the amino methacrylate content. Since this particular component is relatively costly, there is a continuing search to improve the pour depressancy and antioxidant properties of these dialkylaminoalkyl containing polymers without increasing the dialkylaminoalkyl methacrylate content or alternatively producing an interpolymer in which the dialkylaminoalkyl methacrylate content can be decreased without an equivalent reduction in detergent and antioxidant properties.